With the introduction of new materials in the CMOS gate stacks, such as metal and high-k materials, etching has to address new challenges. Some challenges include process selectivity to avoid formation of silicon recesses and to obtain a low surface roughness, gate-etch anisotropy, atomic or multi-atomic layer scale control of the etching rate, absence of residues, and cleaning of the reactor walls after the process.
The critical dimensions in advanced gate stacks have to be tightly controlled. This control requires a perfect wafer-to-wafer reproducibility. However, process drifts, which can generate changes in etch rates, etching profiles, etching selectivity, etching uniformity, and more generally of the process performance, are often observed in front-end etching processes. These process drifts can often be attributed to changes in the reactor wall conditions, e.g., the chemical composition of the reactor walls. For example, after depositing a metal gate stack (Si/TiN/HfO2) on a substrate, hafnium oxide and titanium oxide residues may also coat the chamber walls. F2, NF3, and other halogens are typically used to remove any such coatings deposited on chamber walls. See, e.g., U.S. Pat. App. Pub. No. 2005/082002 to Kimura et al. which uses F2 and NO to clean Si-containing films from a film-forming apparatus.
Plasma based processes are typically the method used to etch metal or metal oxide materials or remove un-wanted deposits thereof from a reactor. See, e.g., a cyclic plasma Bosch process using a fluorine-containing etching fluid, such as PF3, and an unsaturated hydrogen-containing polymer deposition fluid (WO2015/194178 to L'Air Liquide, S.A.); plasma etching Si using PF5 or F2 (JP2007141918 to Matsushita Electric Ind. Co. Ltd.); BCl3 based plasmas exhibit promising plasma chemistries to etch high-k materials and, in particular, HfO2, with a high selectivity over SiO2 and Si substrates (Sungauer et al., J. Vac. Sci. Technol. B 25 (2007) 1640-1646); chlorine plasma is found to chemically etch ZrO2 thin films in an electron cyclotron resonance reactor (Sha et al., J. Vac. Sci. Technol., A 20 (2002) 1525); to improve the etching selectivity of ZrO2, BCl3 was added to a Cl2 plasma to enhance the ZrO2 etch rate while suppressing the silicon etch rate (Sha et al., J. Vac. Sci. Technol., A 21 (2003) 1915); and an investigation of the etching characteristics (etch rate, selectivity to Si) of ZrO2 thin films in the HBr/SF6 high density plasma system (Woo et al., Thin Solid Films 517 (2009) 4246-4250).
Dry plasma etching processes have some disadvantages such as the cost of the equipment, the use of toxic or corrosive gases, and potential damage to the underlying substrate.
H. Schafer (Z. Anorg. Allg. Chem. 1960, 305, 341) and W. A. Jenkins (J. Inorg. Nucl. Chem. 1959, 11, 163) described the thermal etching process of Tantalum oxide (Ta2O5) at temperatures between 200 and 350° C. according to the equation Ta2O5(s)+3TaCl5(g)→5 TaOCl3(g). The reaction is endothermic (˜35 kcal/mol) and an increase of the etching rate with temperature was observed. Nonetheless, the etching rate was too slow (˜6×10−2 A/Cy) to be suitable to replace existing plasma based processes. Knapas et al. (Chem. Vap. Deposition 2009, 15, pp. 269-273) found that NbCl5 etches Nb2O5 film producing volatile NbOCl3. Mercier et al. report that the NbCl5 also reacts with the silica sidewalls of the reactor (Surface and Coatings Technology, 260, 2014, pp. 126-132).
U.S. Pat. No. 6,143,191 describes a method for thermally etching an Iridium containing material using XeF2 as the etching co-reactant. U.S. Pat. No. 6,284,052 describes a method of cleaning metal deposition by-products from interior surfaces of a chemical vapor deposition (CVD) chamber by introducing hydrolysed hexafluoroacetylacetonate (Hhfac) vapor into the chamber to volatilize the oxidized metal deposition by-products.
U.S. Pat. No. 6,077,451 describes a method of etching of silicon oxide (SiO2) by using Xenon fluoride like XeF4, XeF6, OF2, O2F2, and IF6.
U.S. Pat. Nos. 9,130,158 and 9,391,267 to Lam Research Corp. disclose a method for etching a stack with at least one metal layer in one or more cycles by transforming part of the metal layer into a metal oxide, metal halide, or lattice damaged metallic site and providing an organic solvent vapor and an organic ligand solvent to form a volatile organometallic compound.
A need remains for improved gaseous thermal etching and chamber cleaning processes.
Notation and Nomenclature Certain abbreviations, symbols, and terms are used throughout the following description and claims, and include:
As used herein, the term “remove,” “removing,” “cleaning,” “etch,” or “etching” refers to a process of forming a volatile reaction product by contacting a non plasma vapor with a layer that is to be removed from an underlying substrate (i.e., a dry non-plasma etch process).
The term “selectivity” means the ratio of the etch rate of one material to the etch rate of another material. The term “selective etch” or “selectively etch” means to etch one material more than another material, or in other words to have a greater or less than 1:1 etch selectivity between two materials.
As used herein, the indefinite article “a” or “an” means one or more.
As used herein, the terms “approximately” or “about” mean±10% of the value stated.
As used herein, the term “ranges from . . . inclusive” or “inclusively ranges from . . . ” means that the range includes the endpoints. In other words, “x ranges from 2 to 6 inclusive” means that x may be 2 or 6, as well as all points in between.
As used herein, the abbreviation A refers to an Angstrom, which is a unit of length equivalent to 0.1 nm.
As used herein, 1 Torr is a unit of pressure equivalent to 133.3 Pa.
The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements may be referred to by these abbreviations (e.g., S refers to sulfur, Si refers to silicon, H refers to hydrogen, etc.).
Please note that the films or layers deposited, such as Vanadium oxide, are listed throughout the specification and claims without reference to their proper stoichiometry (i.e., VO2, V2O3, V2O5). The layers may include pure (M) layers, carbide (MoCp) layers, nitride (MkNl) layers, oxide (MnOm) layers, or mixtures thereof, wherein M is an element and k, l, m, n, o, and p inclusively range from 1 to 6 inclusive. For instance, Vanadium oxide is VkOl, where k and l each range from 0.5 to 5 inclusive. More preferably Vanadium oxide is VO2, V2O3 or V2O5. The oxide layer may be a mixture of different binary or ternary oxides layers. For example, the oxide layer may be SrTiOx, BaTiOx, HfZrOx, HfTiOx, HfYOx, ZrYOx, TiAlOx, ZrErOx, ZrLaOx, ZrDyOx, HfDyOx, HfLaOx, TiErOx, TiYOx, wherein x ranges from 1 to 6 inclusive. The oxide layer may be a stack of different oxides layers, such as for example HfO2/Al2O3 nanolaminates. Any referenced layers may also include a Silicon oxide layer, Si3Om, wherein n ranges from 0.5 to 1.5 inclusive and m ranges from 1.5 to 3.5 inclusive. More preferably, the silicon oxide layer is SiO2 or SiO3. The silicon oxide layer may be a silicon oxide based dielectric material, such as organic based or silicon oxide based low-k dielectric materials such as the Black Diamond II or III material by Applied Materials, Inc. Alternatively, any referenced silicon-containing layer may be pure silicon. Any silicon-containing layers may also include dopants, such as B, C, P, As and/or Ge.